Question

表一

===================
id    name
-------------------
1     m
2     m
3     a
4     u
5     g

表二

===================
id    name
-------------------
8     m
9     m
10    u
11    a
12    x
15    m

预期结果

===================
1     m     8
2     m     9
3     a     11
4     u     10

我需要通过名称在表2中找到与表1相关联的id。但表2中的ID必须不同。

如果我加入，我会收到错误的交叉点：

select t1.id as i1, t1.name, t2.id as i2 from t1
 join t2 on t1.name = t2.name



 i1  name i2
--------------------
'1','m','8'
'2','m','8'
'1','m','9'
'2','m','9'
'4','u','10'
'3','a','11'
'1','m','15'
'2','m','15'

我需要这个用于来自不同系统的表同步。

Answer 1

您可以使用以下查询：

SELECT t1.id, t1.name, t2.id
FROM (
   SELECT id, name,
          @rn1 := IF(@n = name, @rn1 + 1,
                    IF(@n := name, 1, 1)) AS rn1
   FROM Table1
   CROSS JOIN (SELECT @rn1 := 0, @n := '') AS vars
   ORDER BY name, id) AS t1
INNER JOIN (
   SELECT id, name,
          @rn2 := IF(@n = name, @rn2 + 1,
                    IF(@n := name, 1, 1)) AS rn2
   FROM Table2
   CROSS JOIN (SELECT @rn2 := 0, @n := '') AS vars
   ORDER BY name, id
) AS t2 ON t1.name = t2.name AND t1.rn1 = t2.rn2
ORDER BY t1.id

查询使用变量来模拟ROW_NUMBER()窗口函数，目前在MySQL中不可用。变量@rn1，@rn2枚举属于相同 name分区的记录，其顺序由id字段确定。

Demo here

MySql按顺序连接两个表

1 个答案: